Device having a sensor arrangement for determining the ambient-air quality and an arrangement of ozone sensors upstream and downstream of a radiator which is coated with a catalyst material, and method for operating a device of this type
For reasons of environmental and personal protection, the levels of pollutants which result from motor vehicles with an internal combustion engine or from the generation of energy using stationary combustion installations have to be reduced considerably.
A new approach aimed at reducing the levels of pollutants consists in actively removing pollutants not directly from the exhaust-gas stream from a combustion installation, but rather from the ambient air. This route is promising in particular for the removal of ground-level ozone, which has a considerable influence on how people feel on account of its strongly oxidizing action. Ozone itself is not a gas which is emitted directly and therefore cannot be removed in the exhaust-gas stream. It is formed when nitrogen oxides are present in outside air under solar radiation, on account of the UV component of this radiation, as a result of complex photochemical reaction equilibria.
Since ozone is extremely reactive, it can easily be broken down quantitatively by means of a catalyst system through which air flows. These catalysts are extremely stable, since there is no need for any direct action of strong oxidation catalysts, which are highly sensitive to poisoning, such as for example platinum. Systems which substantially effect adsorption of the ozone on a surface are sufficient; this ozone then breaks down instantaneously to form oxygen.
Catalyst systems of this type have long been in use in passenger aircraft which fly close to the ozone layer, where they are used to treat the air which is passed into the passenger compartment. Recently, such systems have also been deployed in motor vehicles. Here, the radiator of the vehicle is coated with the catalyst. The large quantities of air flowing through the radiator are quantitatively cleaned of ozone, i.e. the vehicle cleans the ambient air.
A system of this type represents a component of relevance in terms of the exhaust gas. The legislators in increasing numbers of countries are imposing an on-board diagnosis system for all components which are relevant to the exhaust gas. Therefore, a suitable sensor system is also required for an ozone-cleaning system.
Particularly in densely populated areas, local pollutant peaks occur and have an adverse effect at least on the feeling of wellbeing if not even on the health of people. Such high pollutant concentrations may occur, for example, in underpasses or tunnels. Traffic queues may also be considered critical in this respect.
Conventional vehicle ventilation systems supply highly polluted ambient air to the interior of the vehicle and therefore to the driver of the vehicle. However, it is already known from the prior art to use suitable sensors to detect an extremely high level of pollutants in the ambient air. As a function of this, the supply of air to the interior of the vehicle is regulated or interrupted from time to time. Sensors of this type are sensitive in particular to gases such as NOx, CO and HC.
A control operation of this type may be initiated as a result of the vehicle driving into a busy road tunnel or as a result of a vehicle stopping behind a truck at traffic lights. Therefore, a very rapid response of the sensor arrangement is particularly necessary.
The object of the invention is to provide an improved ambient-air quality sensor arrangement and diagnosis in particular in a motor vehicle.
According to the invention, the device according to the invention, in particular for use in a motor vehicle, is designed with a sensor arrangement, which controls an air-conditioning unit, for determining the ambient-air quality and an arrangement of ozone sensors upstream and downstream of a radiator, in particular of the motor vehicle, which is coated with a catalyst material for detecting the conversion rate of the conversion of ozone into oxygen which is effected by the catalyst.
Therefore, the invention proposes a sensor arrangement which combines both the task of ambient-air quality measurement and the task of functional diagnosis for an ozone converter with one another and therefore makes it possible to utilize synergy effects which result. The use of sensors of similar types for both applications, namely ambient-air quality measurement and ozone conversion functional diagnosis, and the resulting substantially identical demands imposed on the control and evaluation electronics, lead to space and cost savings.
In an advantageous refinement of the invention, the sensor arrangement for determining the air quality and the ozone sensor for determining the ozone level upstream of the radiator are arranged in a common first airstream. This on the one hand saves space and on the other hand ensures that all the values determined originate from the same location. Therefore, it is on the one hand advantageously possible for the ozone level to be included in the determination of the air quality and on the other hand for the measured values for the air quality to be used to correct the measured ozone level, since the ozone sensors have a cross-sensitivity with respect to other gases, and therefore the ozone measured value is subject to certain error boundaries.
In a particularly advantageous refinement of the invention, both the first airstream and a second airstream, in which the ozone concentration downstream of the radiator is measured, are accommodated in a common housing, in which, in a particularly advantageous configuration of the device according to the invention, a control unit which processes the signals from the sensors is also arranged. This advantageously allows the signals from all the sensors to be processed from just one, centrally arranged control unit. In a development of the invention, this control unit can also be used to control heating elements arranged at the sensors.
In an advantageous refinement of the invention, all the signals and supply voltages can be passed via a single plug connector and therefore via only a single cable, which considerably simplifies installation in particular in a motor vehicle.
In principle, it is also possible for a dedicated airstream passage with a specific sensor arranged therein to be provided for each gas which is to be detected. It is essential for the invention for all the passages to run in one housing. In addition to ozone, examples of gases which are to be detected may be CO, NOx or HC.